Key points
SICK UK’s Industrial Instrumentation specialist, Darren Pratt, looks at the versatility of guided micro-wave radar technology in successful level measurement in process industries.
Accuracy in level detection and measurement is highly important in industries where water, oil and other fluids are stored, dispensed into containers of all sizes and/or used in processing and other operations.
There are many applications where precise level detection is critical to productivity and ensuring continuity of process for example, keeping a header tank on a bottle filling line at the optimum level by switching on flow from the main tank and warning of supply problems.
Alternatively, level detection may be a safety measure to prevent spillage risk of dangerous or valuable fluids. Conversely, avoidance of empty tanks may be essential to stop dry running damage to pumps, machine tools and other equipment or even sediment from a tank being flushed into process lines.
Guided microwave radar technology
In seeking an effective solution to these problems, the development of guided microwave radar technology has led to a number of versatile sensing options. They can achieve high performance, unaffected by density or conductivity. In more advanced sensors the presence of foams or coating deposits can be ignored due to the use of special algorithms built into the level sensor.
The consistent accuracy of guided micro-wave radar technology has seen quick adoption and sensor manufacturers are being asked to come up with ways to expand its uses through the adaptation and configuration of the sensor’s probes for different applications.
Guided wave radar fluid level probes can have advantages for example to solve manufacturing challenges.
For example:
- difficult tank shapes, materials or accessibility
- hot fluids that create challenges for the electronic components
- fluids with a very low dielectric constant
- high foaming or even highly corrosive substances.
Fluid difficulties
A particular problem with some process fluids is their low surface tension and high propensity for foaming. Many additives dissolved in the fluids increase foaming properties and there are also cases, such as in beverage manufacture, where foam enhances the finished product, so it is desirable even though it can create measuring difficulties for some technologies.
As a result, standard level technology, such as floats, capacitance, tuning forks and ultrasonics, can struggle when trying to deliver a precise measurement both through the blanketing effect of foam and the difficulty of defining a precise liquid air interface point. Many of these technologies also suffer from filming and coating build-up, or may even not conform to hygiene requirements.
Foam conquered
With the LFP fluid level probe from SICK, for example, accurate measurement in the presence of thick foam is ensured through a patented “foam algorithm” enabling microwave radar probes to see through large amounts of foam and detect the true fluid level.
Excellent success rates and significant cost savings have been demonstrated for vessel level measurement and bottle filling applications in liquids such as milk, beer, paints and detergents in the presence of wet, dense foams. On high-speed filling lines, the wastage caused by under or over-filling and line downtime due to false head tank level readings can be significantly reduced.
Extended probe length
In response to the needs of end-users, fluid level probes have had practical adaptations to meet specific production challenges. For example, as many level measuring applications have long level ranges either in large tanks or slim deep ones, an extended probe length up to four metres can provide accurate measuring options.
Installations with limited headroom above the tank can now be solved using a flexible variant. By substituting a weighted stainless steel rope up to 4m long for the solid probe, to guide the microwave pulse. Installation and handling are very straightforward.
High process temperatures
Remote amplifier models provide a solution for higher process temperatures, up to 180˚C, or where the separation of the probe and electronics provides easier access to the device for setup and diagnostics.
The separation of the probe and amplifier even facilitates autoclaving, a process where the whole tank is removed for deep sterilisation, with the fitted probe provided with a sealed BNC connection.
Low dielectrics, aggressive liquids and awkward tanks
A co-ax tube accessory has shown success with applications where the liquids measured have a very low dielectric (e.g. oils and cutting fluids). They are also suitable for use in tanks which are open topped, have non-metallic walls or metal protrusions inside the tank that could disrupt the sensing of the reflected radar pulse. Here, a stainless steel, perforated sleeve over the probe facilitates measurement of the liquid level.
For use where stainless steel would be rapidly corroded or dissolved by chemical and/or galvanic reaction, such as in metal plating or with hot, concentrated acid solutions, titanium wetted parts can be introduced.
CASE STUDY: Versatility Reduces Downtime for Bottle Filling
For example, at the Nelson facility of Cott Beverages, the world’s largest retailer brand beverage company, the installation of LFP Inox fluid level probes from SICK UK shows how the versatility of the Guided Micro-wave Radar Technology delivered a replacement solution with far-reaching benefits for the whole plant.
Ensuring maximum uptime is a key priority on each of the five filling lines for still and carbonated drinks, as well as two aseptic bottling lines housed in a separate plant on a neighbouring site.
On a typical multi-bottle filler, one litre and 500ml carbonated soft drinks like colas are bottled at around 19,000 units per hour, which allows a 40ms fill-time per unit. The syrup is mixed with water, carbonated, and then fed under pressure to the filling bowl, a ring-shaped header tank above the filling nozzles.
Controlling the level of liquid in the filling bowl is critical to the process as it determines the accuracy of fill. Margins can be squeezed by a run of poor fill. In addition, identifying which conventional level sensor was faulty, replacing it, testing, calibrating and cleaning could take around four hours of downtime, equating to the filling of about 80,000 bottles.
Sick LFP Inox hygienic level sensors with IO-Link offered the improvements in performance and data output required. Cott Beverages then worked with SICK technical team to determine the correct specification.
IO-Link for better control
Connection to the three sensors is made via IO-Link via a single gateway integrating all three sensors to the Profibus network. This provides digital access to diagnostic data in each sensor allowing monitoring of the operating status of an individual sensor, and an alarm can be triggered before any failure.
In the event of a fault developing with one of the sensors, the alarm and operator instructions on the filler’s HMI control panel facilitate the switching out of the faulty device. An average level of the two remaining sensors is maintained until an assessment can be made during routine maintenance downtime.
The SICK LFP microwave sensors also have their own LED and digital readout, so faults can easily be detected either on the HMI or on the filler bowl itself.
A two-metre long probe is kept in the back-up spares to fit each application on the plant. In addition, the LFP’s self-teach simplifies set up. The unit can be fitted at the press of a button.
Trials showed that the a sensor replacement could be completed during the one hour Clean In Place (CIP) phase between production runs; a quarter of the time it took with the previous level sensing technology.
